These studies are concerned with how premature maternal separation affects development. They are based on previous studies from this laboratory which have demonstrated physiological as well as behavioral changes in 2 week old rat pups removed from their mothers for 24 hours. Physiological studies will include electrophysiological recordings of sleep states and measures of biogenic amine regulation as well as cardiac and respiratory rate measures. The behavior of separated pups will be studied and compared with mothered littermates. A major focus will be upon analytic experiments to determine the mechanisms by which particular aspects of the mother-pup interaction are related to a given physiologic or behavioral response to separation. Rat pups will be studied both in the acute period of the day or two following separation at 2 weeks postnatal age and also during adaptation to permanent maternal separation in the ensuing days or weeks. Long-term effects will be studied in adult rats with histories of premature separation from the mother. These experimental subjects will be compared with normally-reared adults in experiments designed to test the hypothesis that early separation sensitizes developing neural regulatory systems to adult experiences which repeat critical aspects of the early deprivation experience. The aim is to develop an animal model system for detailed study of the biological impact of early deprivation and to increase understanding of the normal mother-infant relationship.